Channel transitions that a mobile terminal makes when the mobile terminal performs packet communications with a base station will be described below. FIG. 1 is a diagram illustrative of channel transitions according to a relevant communication process. It is assumed that the communication process is based on W-CDMA (Wideband Code Division Multiple Access). W-CDMA is disclosed in WO2004/019637, for example. It is also assumed that a base station can be connected to a server that stores web pages through a mobile telephone network and the Internet.
When a mobile terminal completes its positional registration in a base station, the mobile terminal is brought into a standby mode waiting for an incoming call or an outgoing call while being kept idle with minimum electric power consumption. When the user operates the mobile terminal to enter a command to request a web page, the mobile terminal changes into a CELL-DCH (Dedicated Channel) mode wherein the mobile terminal starts packet communications with the base station and sends information representing a request for the web page to the base station. When the mobile terminal receives web page data from a server on the network via an individual channel assigned by the base station, the mobile terminal displays an image based on the web page data on its screen.
Thereafter, if no packet communications take place with the base station upon elapse of a certain time, then the mobile terminal releases individual channels and makes channel transitions in order to increase the frequency usage efficiency. Specifically, the mobile terminal makes channel transitions successively from a CELL-DCH mode to a CELL-FACH (Forward Access Channel) mode to a CELL-PCH (Paging Channel) mode finally to an IDLE mode. If packet communications take place while in the CELL-FACH mode, or CELL-PCH mode, or the IDLE mode, then the mobile terminal immediately makes a channel transition to the CELL-DCH mode.
As described above, the mobile terminal makes channel transitions successively from the CELL-DCH mode to the CELL-FACH mode to the CELL-PCH mode to the IDLE mode in order to increase the frequency usage efficiency. According to a communication sequence for establishing a call connection between the mobile terminal and the base station, the communication volume of control information is greater when the mobile terminal makes a channel transition from the IDLE mode to the CELL-DCH mode than when the mobile terminal makes a channel transition from the CELL-FACH mode or from the CELL-PCH mode to the CELL-DCH mode. In order to prevent the communication volume of control information from increasing when the mobile terminal resumes packet communications after having finished packet communications at one time, the mobile terminal is kept in the CELL-FACH mode or in the CELL-PCH mode for a certain time, so that the mobile terminal is kept on standby in readiness for resuming packet communications quickly.
In the CELL-FACH mode or the CELL-PCH mode, however, the mobile terminal consumes electric power to keep itself ready for packet communications though it actually does not perform packet communications. Recently, there has been proposed a method of controlling channel transitions called a Fast Dormancy function as communication specifications for 3GPP for the purpose of reducing electric power consumption.
FIG. 2 is a diagram illustrative of channel transitions at the time when the Fast Dormancy function is performed. The Fast Dormancy function causes a mobile terminal to make a channel transition from the CELL-DCH mode to the IDLE mode if no packet communications take place for a certain time after the mobile terminal has performed packet communications. According to the Fast Dormancy function, since the mobile terminal is not kept on standby temporarily in the CELL-DCH mode and the IDLE mode according to the channel transition control described with reference to FIG. 1, electric power consumption required to maintain the mobile terminal in packet communications is eliminated. The electric power consumption of the mobile terminal becomes progressively smaller in the order of the CELL-DCH mode, the CELL-PCH mode, and the IDLE mode.